/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_fir_q31.c
*
* Description:	Q31 FIR filter processing function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
*
* Version 0.0.5  2010/04/26
* 	 incorporated review comments and updated with latest CMSIS layer
*
* Version 0.0.3  2010/03/10
*    Initial version
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup FIR
 * @{
 */

/**
 * @param[in] *S points to an instance of the Q31 FIR filter structure.
 * @param[in] *pSrc points to the block of input data.
 * @param[out] *pDst points to the block of output data.
 * @param[in] blockSize number of samples to process per call.
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 * \par
 * The function is implemented using an internal 64-bit accumulator.
 * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
 * Thus, if the accumulator result overflows it wraps around rather than clip.
 * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.
 * After all multiply-accumulates are performed, the 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result.
 *
 * \par
 * Refer to the function <code>arm_fir_fast_q31()</code> for a faster but less precise implementation of this filter for Cortex-M3 and Cortex-M4.
 */

void arm_fir_q31(
    const arm_fir_instance_q31* S,
    q31_t* pSrc,
    q31_t* pDst,
    uint32_t blockSize)
{
	q31_t* pState = S->pState;                     /* State pointer */
	q31_t* pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
	q31_t* pStateCurnt;                            /* Points to the current sample of the state */


#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	q31_t x0, x1, x2;                              /* Temporary variables to hold state */
	q31_t c0;                                      /* Temporary variable to hold coefficient value */
	q31_t* px;                                     /* Temporary pointer for state */
	q31_t* pb;                                     /* Temporary pointer for coefficient buffer */
	q63_t acc0, acc1, acc2;                        /* Accumulators */
	uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
	uint32_t i, tapCnt, blkCnt, tapCntN3;          /* Loop counters */

	/* S->pState points to state array which contains previous frame (numTaps - 1) samples */
	/* pStateCurnt points to the location where the new input data should be written */
	pStateCurnt = &(S->pState[(numTaps - 1u)]);

	/* Apply loop unrolling and compute 4 output values simultaneously.
	 * The variables acc0 ... acc3 hold output values that are being computed:
	 *
	 *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
	 *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
	 *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
	 *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]
	 */
	blkCnt = blockSize / 3;
	blockSize = blockSize - (3 * blkCnt);

	tapCnt = numTaps / 3;
	tapCntN3 = numTaps - (3 * tapCnt);

	/* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
	 ** a second loop below computes the remaining 1 to 3 samples. */
	while(blkCnt > 0u) {
		/* Copy three new input samples into the state buffer */
		*pStateCurnt++ = *pSrc++;
		*pStateCurnt++ = *pSrc++;
		*pStateCurnt++ = *pSrc++;

		/* Set all accumulators to zero */
		acc0 = 0;
		acc1 = 0;
		acc2 = 0;

		/* Initialize state pointer */
		px = pState;

		/* Initialize coefficient pointer */
		pb = pCoeffs;

		/* Read the first two samples from the state buffer:
		 *  x[n-numTaps], x[n-numTaps-1] */
		x0 = *(px++);
		x1 = *(px++);

		/* Loop unrolling.  Process 3 taps at a time. */
		i = tapCnt;

		while(i > 0u) {
			/* Read the b[numTaps] coefficient */
			c0 = *pb;

			/* Read x[n-numTaps-2] sample */
			x2 = *(px++);

			/* Perform the multiply-accumulates */
			acc0 += ((q63_t) x0 * c0);
			acc1 += ((q63_t) x1 * c0);
			acc2 += ((q63_t) x2 * c0);

			/* Read the coefficient and state */
			c0 = *(pb + 1u);
			x0 = *(px++);

			/* Perform the multiply-accumulates */
			acc0 += ((q63_t) x1 * c0);
			acc1 += ((q63_t) x2 * c0);
			acc2 += ((q63_t) x0 * c0);

			/* Read the coefficient and state */
			c0 = *(pb + 2u);
			x1 = *(px++);

			/* update coefficient pointer */
			pb += 3u;

			/* Perform the multiply-accumulates */
			acc0 += ((q63_t) x2 * c0);
			acc1 += ((q63_t) x0 * c0);
			acc2 += ((q63_t) x1 * c0);

			/* Decrement the loop counter */
			i--;
		}

		/* If the filter length is not a multiple of 3, compute the remaining filter taps */

		i = tapCntN3;

		while(i > 0u) {
			/* Read coefficients */
			c0 = *(pb++);

			/* Fetch 1 state variable */
			x2 = *(px++);

			/* Perform the multiply-accumulates */
			acc0 += ((q63_t) x0 * c0);
			acc1 += ((q63_t) x1 * c0);
			acc2 += ((q63_t) x2 * c0);

			/* Reuse the present sample states for next sample */
			x0 = x1;
			x1 = x2;

			/* Decrement the loop counter */
			i--;
		}

		/* Advance the state pointer by 3 to process the next group of 3 samples */
		pState = pState + 3;

		/* The results in the 3 accumulators are in 2.30 format.  Convert to 1.31
		 ** Then store the 3 outputs in the destination buffer. */
		*pDst++ = (q31_t)(acc0 >> 31u);
		*pDst++ = (q31_t)(acc1 >> 31u);
		*pDst++ = (q31_t)(acc2 >> 31u);

		/* Decrement the samples loop counter */
		blkCnt--;
	}

	/* If the blockSize is not a multiple of 3, compute any remaining output samples here.
	 ** No loop unrolling is used. */

	while(blockSize > 0u) {
		/* Copy one sample at a time into state buffer */
		*pStateCurnt++ = *pSrc++;

		/* Set the accumulator to zero */
		acc0 = 0;

		/* Initialize state pointer */
		px = pState;

		/* Initialize Coefficient pointer */
		pb = (pCoeffs);

		i = numTaps;

		/* Perform the multiply-accumulates */
		do {
			acc0 += (q63_t) * (px++) * (*(pb++));
			i--;
		} while(i > 0u);

		/* The result is in 2.62 format.  Convert to 1.31
		 ** Then store the output in the destination buffer. */
		*pDst++ = (q31_t)(acc0 >> 31u);

		/* Advance state pointer by 1 for the next sample */
		pState = pState + 1;

		/* Decrement the samples loop counter */
		blockSize--;
	}

	/* Processing is complete.
	 ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
	 ** This prepares the state buffer for the next function call. */

	/* Points to the start of the state buffer */
	pStateCurnt = S->pState;

	tapCnt = (numTaps - 1u) >> 2u;

	/* copy data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}

	/* Calculate remaining number of copies */
	tapCnt = (numTaps - 1u) % 0x4u;

	/* Copy the remaining q31_t data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}

#else

	/* Run the below code for Cortex-M0 */

	q31_t* px;                                     /* Temporary pointer for state */
	q31_t* pb;                                     /* Temporary pointer for coefficient buffer */
	q63_t acc;                                     /* Accumulator */
	uint32_t numTaps = S->numTaps;                 /* Length of the filter */
	uint32_t i, tapCnt, blkCnt;                    /* Loop counters */

	/* S->pState buffer contains previous frame (numTaps - 1) samples */
	/* pStateCurnt points to the location where the new input data should be written */
	pStateCurnt = &(S->pState[(numTaps - 1u)]);

	/* Initialize blkCnt with blockSize */
	blkCnt = blockSize;

	while(blkCnt > 0u) {
		/* Copy one sample at a time into state buffer */
		*pStateCurnt++ = *pSrc++;

		/* Set the accumulator to zero */
		acc = 0;

		/* Initialize state pointer */
		px = pState;

		/* Initialize Coefficient pointer */
		pb = pCoeffs;

		i = numTaps;

		/* Perform the multiply-accumulates */
		do {
			/* acc =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */
			acc += (q63_t) * px++ * *pb++;
			i--;
		} while(i > 0u);

		/* The result is in 2.62 format.  Convert to 1.31
		 ** Then store the output in the destination buffer. */
		*pDst++ = (q31_t)(acc >> 31u);

		/* Advance state pointer by 1 for the next sample */
		pState = pState + 1;

		/* Decrement the samples loop counter */
		blkCnt--;
	}

	/* Processing is complete.
	 ** Now copy the last numTaps - 1 samples to the starting of the state buffer.
	 ** This prepares the state buffer for the next function call. */

	/* Points to the start of the state buffer */
	pStateCurnt = S->pState;

	/* Copy numTaps number of values */
	tapCnt = numTaps - 1u;

	/* Copy the data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}


#endif /*  #ifndef ARM_MATH_CM0 */

}

/**
 * @} end of FIR group
 */
